Evaluation of the Degradation of Fiber Composites by Integrated Structural Health Monitoring

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The degradation of fiber-reinforced polymers due to cyclic loading is associated with micro defects in the material. Within this project, the implications of micro defects on the propagation of Lamb waves will be investigated. The first objective is to capture qualitatively the effects of micro defects, which are characteristic for fiber-reinforced plastics but not relevant to immediate failure, and the related material degradation on the characteristic properties of Lamb waves. The experimental investigations will analyze the degradation influence on characteristic parameters of the linear wave theory, such as the group velocity, and include the non-linear defect behavior, which is caused e.g. by the interaction of crack surfaces and which may be described by the acoustic nonlinear parameter. It is assumed that reference measurements from undamaged specimens have to be available. The second, far-reaching objective aims at the quantification of these effects. The related experiments address the question whether the extent of the degradation and thus the extent of the damage can be assessed by changes of those parameters, which describe the propagation behavior of Lamb waves.